1. Field of the Invention
This invention relates to a measuring chip for use in, for instance, a surface plasmon resonance sensor for quantitatively analyzing a material in a sample utilizing generation of surface plasmon.
2. Description of the Related Art
In metal, free electrons vibrate in a group to generate compression waves called plasma waves. The compression waves generated in a metal surface are quantized into surface plasmon.
There have been proposed various surface plasmon resonance sensors for quantitatively analyzing a material in a sample utilizing a phenomenon that such surface plasmon is excited by light waves. Among those, one employing a system called xe2x80x9cKretschmann configurationxe2x80x9d is best known. See, for instance, Japanese Unexamined Patent Publication No. 6(1994)-167443.
The plasmon resonance sensor using the Kretschmann configuration basically comprises a dielectric block shaped, for instance, like a prism, a metal film which is formed on one face of the dielectric block and is brought into contact with a sample, a light source emitting a light beam, an optical system which causes the light beam to enter the dielectric block so that the light beam is reflected in total internal reflection at the interface of the dielectric block and the metal film and various angles of incidence of the light beam to the interface of the dielectric block and the metal film including an angle of incidence at which surface plasmon is generated can be obtained, and a photodetector means which is able to detect the intensity of the light beam reflected in total internal reflection at the interface and detect a state of surface plasmon resonance.
In order to obtain various angles of incidence of the light beam to the interface, a relatively thin incident light beam may be caused to impinge upon the interface while deflecting the incident light beam or a relatively thick incident light beam may be caused to impinge on the interface in the form of convergent light or divergent light so that components of the incident light beam impinge upon the interface at various angles. In the former case, the light beam which is reflected from the interface at an angle which varies as the incident light beam is deflected may be detected by a photodetector which is moved in synchronization with deflection of the incident light beam or by an area sensor extending in the direction in which reflected light beam is moved as a result of deflection. In the latter case, an area sensor which extends in directions so that all the components of light reflected from the interface at various angles can be detected by the area sensor may be used.
In such a plasmon resonance sensor, when a light beam impinges upon the interface at a particular angle of incidence xcex8sp not smaller than the angle of total internal reflection, evanescent waves having an electric field distribution in the sample in contact with the metal film are generated and surface plasmon is excited in the interface between the metal film and the sample. When the wave vector of the evanescent waves is equal to the wave number of the surface plasmon and wave number matching is established, the evanescent waves and the surface plasmon resonate and light energy is transferred to the surface plasmon, whereby the intensity of light reflected in total internal reflection at the interface of the dielectric block and the metal film sharply drops. The sharp intensity drop is generally detected as a dark line by the photodetector.
The aforesaid resonance occurs only when the incident light beam is p-polarized. Accordingly, it is necessary to set the light beam to impinge upon the interface in the form of p-polarized light.
When the wave number of the surface plasmon can be known from the angle of incidence xcex8sp at which the phenomenon of attenuation in total internal reflection (ATR) takes place, the dielectric constant of the sample can be obtained. That is,             K      sp        ⁡          (      ω      )        =            ω      c        ⁢                                                      ϵ              m                        ⁡                          (              ω              )                                ⁢                      ϵ            s                                                              ϵ              m                        ⁡                          (              ω              )                                +                      ϵ            s                              
wherein Ksp represents the wave number of the surface plasmon, xcfx89 represents the angular frequency of the surface plasmon, c represents the speed of light in a vacuum, and ∈ m and ∈ s respectively represent the dielectric constants of the metal and the sample.
When the dielectric constant ∈ s of the sample is known, the concentration of a specific material in the sample can be determined on the basis of a predetermined calibration curve or the like. Accordingly, a specific component in the sample can be quantitatively analyzed by detecting the angle of incidence xcex8sp at which the intensity of light reflected in total internal reflection from the interface of the prism and the metal film sharply drops.
In the conventional plasmon resonance sensor of the type described above employing the system described above, it is practically necessary to change sample by sample the metal film to be brought into contact with the sample. Conventionally, the metal film is fixedly formed on a flat and thin dielectric plate as a unit and the unit is removably integrated with a prism-like dielectric block which functions as an optical coupler for causing total internal reflection. The prism-like dielectric block is fixedly provided with respect to the optical system and the unit of the metal film and the dielectric plate is changed sample by sample as a measuring chip.
As a similar apparatus utilizing the phenomenon of attenuation in total internal reflection (ATR), there has been known a leaky mode sensor described in, for instance, xe2x80x9cSpectrum Researchesxe2x80x9d Vol.47, No.1 (1998), pp21 to 23 and pp26 and 27. The leaky mode sensor basically comprises a dielectric block shaped, for instance, like a prism, a clad layer which is formed on one face of the dielectric block, an optical waveguide layer which is formed on the clad layer and is brought into contact with a sample, a light source emitting a light beam, an optical system which causes the light beam to enter the dielectric block at various angles of incidence so that total internal reflection conditions are satisfied at the interface of the dielectric block and the clad layer, and a photodetector means which is able to detect the intensity of the light beam reflected in total internal reflection at the interface and detect an excited state of waveguide mode, i.e., attenuation in total internal reflection (ATR).
In the leaky mode sensor with this arrangement, when the light beam is caused to impinge upon the clad layer through the dielectric block at an angle not smaller than an angle of total internal reflection, only light having a particular wave number and impinging upon the optical waveguide layer at a particular angle of incidence comes to propagate through the optical waveguide layer in a waveguide mode after passing through the clad layer. When the waveguide mode is thus excited, almost all the incident light is taken in the optical waveguide layer and accordingly, the intensity of light reflected in total internal reflection at the interface of the dielectric block and the clad layer sharply drops. That is, attenuation in total internal reflection occurs. Since the wave number of light to be propagated through the optical waveguide layer in a waveguide mode depends upon the refractive index of the sample on the optical waveguide layer, the refractive index and/or the properties of the sample related to the refractive index can be detected on the basis of the angle of incidence at which the attenuation in total internal reflection occurs.
Also in the leaky mode sensor, it is possible to fix a dielectric block with respect to the optical system, to form the clad layer and the optical waveguide layer on another dielectric block to form a measuring chip, and to change the measuring chip sample by sample.
However, when the conventional measuring chips are used, the dielectric blocks have to be integrated with each other by way of refractive index matching fluid in order to prevent a space from being formed between the dielectric blocks to make discontinuous the refractive index between the blocks. Such operation is very troublesome, which makes the conventional measuring chips inconvenient to handle. Especially, in an automated measuring system in which a plurality of measuring chips are loaded on a turret and the turret is rotated to bring the measuring chips in sequence to a measuring position where a light beam is projected onto each measuring chip, loading and unloading the measuring chips take a lot of labor, which is apt to cause deterioration in the measuring efficiency.
Further, the refractive index matching fluid can adversely affect the environment.
In view of the foregoing observations and description, the primary object of the present invention is to provide a measuring chip which is easily replaceable and can eliminate necessity of using refractive index matching fluid.
In accordance with a first aspect of the present invention, there is provided a measuring chip which is used in a measuring apparatus comprising
a dielectric block,
a film layer which is formed on a first face of the dielectric block and is brought into contact with a sample,
a light source which emits a light beam,
an optical system which causes the light beam to enter the dielectric block through a second face thereof so that the light beam is reflected in total internal reflection at the interface of the dielectric block and the film layer and various angles of incidence of the light beam to the interface of the dielectric block and the film layer can be obtained, and
a photodetector means which detects attenuation in total internal reflection by detecting the intensity of the light beam which is reflected in total internal reflection at the interface and goes outside the dielectric block through a third face thereof,
the measuring chip comprising a single dielectric block having all the first to third faces and the film layer integrally formed on the first face of the dielectric block.
In accordance with a second aspect of the present invention, there is provided a measuring chip which is used especially in a surface plasmon resonance sensor comprising
a dielectric block,
a metal film layer which is formed on a first face of the dielectric block and is brought into contact with a sample,
a light source which emits a light beam,
an optical system which causes the light beam to enter the dielectric block through a second face thereof so that the light beam is reflected in total internal reflection at the interface of the dielectric block and the metal film and various angles of incidence of the light beam to the interface of the dielectric block and the metal film can be obtained, and
a photodetector means which detects attenuation in total internal reflection due to plasmon resonance by detecting the intensity of the light beam which is reflected in total internal reflection and goes outside the dielectric block through a third face thereof,
the measuring chip comprising a single dielectric block having all the first to third faces and the metal film layer integrally formed on the first face of the dielectric block.
In accordance with a third aspect of the present invention, there is provided a measuring chip which is used especially in a leaky mode sensor comprising
a dielectric block,
a film layer composed of a clad layer which is formed on a first face of the dielectric block and an optical waveguide layer which is formed on the clad layer and is brought into contact with a sample,
a light source which emits a light beam,
an optical system which causes the light beam to enter the dielectric block through a second face thereof so that the light beam is reflected in total internal reflection at the interface of the dielectric block and the metal film and various angles of incidence of the light beam to the interface of the dielectric block and the metal film can be obtained, and
a photodetector means which detects attenuation in total internal reflection due to excitation of waveguide mode in the optical waveguide layer by detecting the intensity of the light beam which is reflected in total internal reflection and goes outside the dielectric block through a third face thereof,
the measuring chip comprising a single dielectric block having all the first to third faces and the metal film layer integrally formed on the first face of the dielectric block.
These measuring chips are preferably provided with a sample holder mechanism for holding the sample on the film layer. Specifically, the sample holder mechanism may comprise a member which defines above the film layer a space having closed side walls. It is further preferred that the space is flared upward. In this case, it is preferred that the inner surface of the member which defines above the film layer a space having closed side walls is smoothly merged with the first face of the dielectric block on which the film layer is formed.
Further it is preferred that the dielectric block be polygonal such as a rectangle in a horizontal cross-section. In this specification, xe2x80x9cthe horizontal cross-sectionxe2x80x9d means a cross-section taken along a plane perpendicular to the vertical direction of the block in which the block is positioned in operation of the measuring chip.
When the dielectric block is polygonal in a horizontal cross-section, it is preferred that corners of the polygonal be rounded in at least one horizontal plane. The polygonal may be rounded at corners between two adjacent side surfaces thereof, at corners between two adjacent side surfaces and the bottom surface, and at both the corners.
Further, when the dielectric block is polygonal in a horizontal cross-section, it is preferred that the dielectric block is tapered downward so that the cross-sectional area becomes larger upward. In this case, it is preferred that the inclined side surfaces of the dielectric block be at 3 to 15xc2x0 to the vertical axis of the dielectric block.
Preferably the dielectric block is formed of, for instance, glass or transparent resin. When the dielectric block is formed of transparent resin, it is preferred that the sample holder mechanism be formed integrally with the dielectric block.
Further, it is preferred that a sensing medium which makes bonding reaction with a particular material in the sample be fixed on the film layer.
In the measuring chip in accordance with the present invention since the single dielectric block has all the light incident face, the light emanating face and the face on which the film layer is formed and functions as an optical coupler, the measuring chip need be coupled with or decoupled from another member and accordingly, can be easily and quickly replaced.
That is, unlike the prior art, the measuring chip of the present invention need not be coupled with another dielectric block (as an optical coupler) by way of refractive index matching fluid, and accordingly it is very easy to handle.
Further, since it is not necessary to use the refractive index matching fluid, adverse influence of the fluid on the environment can be avoided.
When the sample holder mechanism comprises a member which defines above the film layer a space which has closed side walls and is flared upward, the film layer can be uniform in thickness. That is, since the film layer is generally formed by deposition, when the sample holder mechanism is of such a shape, the film layer can be uniformly formed without being adversely affected by the sample holder mechanism.
Further, when the inner surface of the member which defines above the film layer a space having closed side walls is smoothly merged with the first face of the dielectric block on which the film layer is formed, plastic injection molding of the dielectric block/sample holder mechanism unit is facilitated since ejection of the products from the injection mold becomes smoother, whereby defective products can be reduced.
When the dielectric block is polygonal in a horizontal cross-section and the corners of the polygonal are rounded in at least one horizontal plane, plastic injection molding of the dielectric block/sample holder mechanism unit is facilitated since ejection of the products from the injection mold becomes smoother, whereby defective products can be reduced.
Further, when the dielectric block is polygonal in a horizontal cross-section and is tapered downward so that the cross-sectional area becomes larger upward, positioning of the measuring chip on the measuring apparatus is facilitated.
That is, by forming a plurality of polygonal holes in a horizontal table of the measuring apparatus and holding the measuring chips by inserting the chips into the holes, the dielectric block can be automatically set in a predetermined direction in a horizontal plane and held there through engagement of polygons.
By the same arrangement, the measuring chips can be automatically positioned also in the vertical direction.
These inventors have found that when the inclined side surfaces of the dielectric block is at 3 to 15xc2x0 to the vertical axis of the dielectric block, the measuring chip can be especially accurately positioned, the reason for which will become apparent later.